Method for reducing sludge deposition of fuel oils



United States Patent Ofiiice 3,006,842 Patented Oct. 31, 1961 3,006,842 METHOD FOR REDUCING SLUDGE DEPOSITION OF FUEL OILS Robert Greatorex and Demetrios Theodore Emmanuel Zalichi, Sunbnry-on-Thames, and William Arthur Partridge, London, England, assignors to The British letroleum Company Limited, London, England, a British joint-stock corporation No Drawing. Filed July 20, 1959, Ser. No. 828,065

Claims priority, application Great Britain July 23, 1958 6 Claims. (Cl. 208177) Residual fuel oils, i.e. fuel oils consisting of or containing petroleum residues, have a tendency to deposit a waxy sludge on storage and in certain circumstances this can cause difficulties, e.g. where in use the fuel oil has to be passed through a screen or strainer. Such difiiculties arise mainly with fuels or Class E, British Standards Specification No. 2869:1957, which are intended to be handled in unheated storage.

We have now found a method whereby this tendency to deposit a sludge can be reduced, Without any significant adverse effect on other desirable properties of the oil, such as pour point and viscosity.

. The invention consists in chilling a residual fuel oil from an upper temperature of at least 110 F., preferably at least 120 F., especially at least 140 F., to a lower temperature not higher than 90 F., preferably not higher than 70 F., at a rate of at least 0.1 F., preferably at least 1 F., per minute.

Residual fuel oils are normally prepared by blending residual materials from distillation and cracking processes and materials discarded during the production of lubricating oils, with lighter components, such as kerosene or gas oil. This blending is carried out at an elevated temperature, usually of the order of 140 F. or higher. Where, therefore, the method of the invention is to be applied to fuel oils which have just been blended, it will not normally be necessary to preheat them.

The chilling may be conveniently effected by passing the fuel oil through conventional heat exchanging equipment, cooled by a flow of cold water or other suitably available cold fluid.

A number of examples of the invention will now be described.

EXAMPLE 1 A fuel oil (A) having a Redwood I viscosity at 100 F. of 199 seconds and a pour point of 15 F. was used in this example. When fuel oil A was cooled at a slower rate than 0.1 F. per minute a waxy deposit or sludge was subsequently deposited and the fuel oil was not filterable. Samples of the same fuel oil when cooled according to the method of the invention were filterable and remained so after a prolonged storage at ambient It can be seen from the above results that the pour point of the oil will be no worse, and indeed may be improved, by chilling the fuel oil according to the meth- 0d of the invention and that the chilling causes no significant change in the viscosity of the oil.

The above example was carried out in the laboratory. Examples 2, 3 and 4 below were carried out in a pilot plant consisting of a 5 gallon oil reservoir connected via a 0600 gallon/hour variable stroke pump to a cooling coil encased in a 40 gallon drum with a return to the feed reservoir. A /2" pipe was used throughout and the cooling coil was 18 arranged in four full turns. The oil to be treated was placed in the reservoir and the 40 gallon drum was filled with a suitable cooling medium such as cold water. The oil in the reservoir was heated by an immersion heater to the required upper temperature and the oil was circulated round the system. The cooling rate, as measured by the temperature drop in the reservoir, was adjusted by varying either the oil level in the reservoir, the circulation rate, or the cooling medium temperature.

EXAMPLE 2 In this example another fuel oil (B) was used having a Redwood I viscosity at F. or 214 seconds and a pour point of 25 F. This fuel oil did not pass the filtration test. When cooled at a rate slower than 0.1 F. per minute the filterability of the oil remained poor and a Waxy sludge was deposited. Samples of fuel oil B were chilled from F. to 90 F. at rates of 1 F. and 7 F. per minute. The chilled samples were filter able, contained no sludge and showed no significant change in viscosity or pour point after storage at ambient temperature for 16 weeks. The results are summarised in Table II.

Table II Heat treatment of fuel 011 B Kinematic Pour Filtration test Sludge vispoint Cooling Cooling Storcosit F.

range rate F./ age at 70 F. minute time F. cs.

weeks 16 Not filterable 111 25 -65 01 4 do Present- 110-90 1 16 Filterable None 114.4 30 110-90 16 do 0 112.8 10

EXAMPLE 3 In this example another fuel oil (C) was used having a Redwood I viscosity at 100 F. of 201 seconds and a pour point of 20 F.- Fuel oil C failed the filtration test. Samples of the fuel oil were chilled at various It will be seen that the treatment according to the invention in all cases resulted in an improvement in the filterability of the fuel oil although chilling rates below 1 F. did not always prevent sludge deposition. Consequently, rates of 1 F. per minute or faster are to be preferred.

EXAMPLE 4 In this example a fuel oil (D) was used having a viscosity at 100 F., of 212 seconds Redwood I and apour point of 25 F. The results of the treatment are given in Table IV.

Table IV Heat treatment of fuel oil D Kinematic Pour Cooling Cooling Stor- Filtration test Sludge viscosity point range rate age at 70 F. F.

F. F./ time cs.

minute weeks 6 Not filterable 115. 8 25 120-65 01 3 ..do Present. 150-80 1 6 Filterable None. 117. 4 150-80 6 6 do do 121. 4

EXAMPLE 5 Storage in all the above examples was at a temperature of 651-5 F. Parallel work has been carried out on samples stored under conditions of varying temperature in the range40 F.-95 F. to provide a more rigorous test of stability. The result are given in Table V below.

The filtration test referred to in the above examples was carried out as follows:

The oil was forced under a constant pressure of 5 psi. and at a constant temperature in the region of 65 1 5 F. through a filter element of 1 diameter, consisting of 10 layers of 200 mesh wire gauze. The taken for 4 ml. and 160 ml. of the oil to flow through the filter were measured, and the ratio of times,

(Time of flow of 160 ml.) (Time of flow of 80 ml),

compared with the ratio of volumes,

The conditions of the test are such that any reduction in the rate of flow of the oil through the filter is due to the filter blocking propensities of the oil. Therefore a time ratio of 2 indicates that the oil was filterable whereas a time ratio substantially greater than 2 or the complete cessation of oil flow through the filter indicates that the oil was not filterable.

The determination of pour points according to IP 15/55 and of viscosities by IP 70/57 or 71/58 entails preheating the samples to F. and 212 F. respectively. As this procedure might destroy the effects of chilling, the determinations in the above examples were carried out without preliminary heat treatment.

We claim:

1. A method of reducing the tendency of a residual fuel oil to deposit a waxy sludge on storage, which consists in chilling the residual fuel oil from an upper temperature of at least 110 F. to a lower temperature not higher than 90 F., at a rate of at least 0.1 E. per minute.

2. A method according to claim 1, in which the rate of chilling is at least 1 F. per minute.

3. A method according to claim 1, in which the upper temperature is at least F.

4. A method according to claim 3, in which the upper temperature is at least F.

5. A method according to claim 1, in which the lower temperature is not higher than 70 F.

6. A method according to claim 1, in which the chilling is effected by passing the fuel oil through heat exchanging equipment chilled by a flow of cold liquid.

References Cited in the file of this patent UNITED STATES PATENTS 64,855 Finn May 21, 1867 1,953,353 Lazar et a1. Apr. 3, 1934 1,957,954 Haeck May 8, 1934 2,249,884 Carney July 22, 1941 2,315,935 Child Apr. 6, 1943 2,365,256 Edv'ai'sson Dec. 19, 1944 2,572,425 Andersson Oct. 23, 1951 2,951,037 ODonnel et a1 Aug. 30,, 1960 

1. A METHOD OF REDUCING THE TENDENCY OF A RESIDUAL FUEL OIL TO DEPOSIT A WAXY SLUDGE ON STORAGE, WHICH CONSISTS IN CHILLING THE RESIDUAL FUEL OIL FROM AN UPPER TEMPERATURE OF AT LEAST 110*F. TO A LOWER TEMPERATURE NOT HIGHER THAN 90*F., AT A RATE OF AT LEAST 0.1*E. PER MINUTE. 